The present invention relates to a method of decelerating a marine propulsion system during an emergency stop maneuver, whereby the marine propulsion system comprises a combustion engine, a propeller shaft and an interposed three shaft birotatory reduction gear system, comprising a synchromesh coupling and a counter rotation coupling. The birotatory reduction gear system is switchable by a control switch to an idling position, a forward drive position and a backward drive position, whereby the control switch also allows adjustment of the number of revolutions and output of the combustion engine.
In general, marine propulsion systems are comprised of a three shaft birotatory reduction gear system which is interposed between the combustion engine and the propeller shaft. In these reduction gear systems the toothed wheels are always in engagement. The switching of the reduction gear system is achieved by engagement or disengagement of hydraulically activated couplings. The couplings are activated from the bridge via a control switch and corresponding electro-hydraulic valves. During idling both couplings are disengaged. When the combustion engine and the propeller shaft are rotating synchronously, a synchromesh coupling is engaged, and when the combustion engine and the propeller shaft are counter rotating, a counter rotation coupling is engaged while at the same time the respective other coupling is disengaged. A disadvantage of such a birotatory reduction gear system is that, when a fast reversal of the direction of rotation is required, a high wear will occur at the coupling disks due to the inertia moments of the couplings, the toothed wheels of the propeller shaft and of the propeller itself. It is thus possible that the combustion engine stalls or will start up again in the reverse direction of rotation.
It is therefore an object of the present invention to provide a method with which a fast reversal of the direction of rotation of the propeller shaft is possible without the couplings of the birotatory reduction gear system wearing at a high rate and without running the risk that the combustion engine will stall or will start up again in the reverse direction of rotation.